The invention relates to a measuring sensor under pre-stress for measuring forces and/or moments.
Measuring sensors are inter alia used as stackable machine elements for the installation into machine or device elements transmitting force and/or moments to measure forces, pressures, accelerations, expansions and moments. Such measuring sensors may be piezoelectric, piezoresistive, optical, capacitive or based on strain gages (DMS). In the following, piezoelectric measuring sensors will be mainly detailed. In these for example, suitable crystals having piezoelectric characteristics in the form of thin discs are incorporated into a sleeve in a centered manner and welded under a membrane exerting a desired pre-stress to the crystals. On the one hand, the pre-stress ensures that the measurement is effected in the linear measuring range of the sensor. On the other hand, also a signal within the linear measuring range of the sensor is generated thereby if negative forces (tensile forces) or vibrations are measured.
However, the level of the measurable tensile forces is too low for many applications with large tensile forces and is limited by the tensile stability of the welding of the membrane to the sleeve of the sensor. To be able to measure higher tensile forces or shearing forces the sensor is incorporated between two adaptor elements by means of a centering sleeve in a centered manner and is placed under an additional pre-stress by means of a suitable screw connection of the adaptor elements.
The arrangement described herein as prior art exhibits certain disadvantages. On the one hand, the overall height of such measuring arrangements is often very large. On the other hand, two centerings (of the crystals in the sensor and of the sensor in one of the adaptor elements) have to be conducted, which is quite elaborate.